Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$86.33	13.730%	$98.1831	$98.18	$98.20	$98.20
Purchase #2	$7.41	11.737%	$8.2797	$8.28	$8.30	$8.30
Purchase #3	$5.32	5.234%	$5.5984	$5.60	$5.60	$5.60
Purchase #4	$23.42	10.341%	$25.8419	$25.84	$25.85	$25.80
Purchase #5	$127.49	9.276%	$139.316	$139.32	$139.30	$139.30
Purchase #6	$165.91	3.327%	$171.4298	$171.43	$171.45	$171.40
Purchase #7	$107.34	3.626%	$111.2321	$111.23	$111.25	$111.20
7 purchase totals =	$523.22		$559.8810	$559.88	$559.95	$559.80